Reversal of acetylcholine potentials in eel electroplaque.

Although the eel electroplaque is a major source of purified acetylcholine (ACh) receptor, the electrophysiological properties of the receptor have not been studied in detail. In particular, the reversal potential for the action of ACh on the postsynaptic membrane has not been measured directly. In order to obtain the reversal potential, ACh was applied iontophoretically from a micropipette onto the innervated membrane. The resulting depolarization (ACh potential) decreased in amplitude as the cell was depolarized, reached zero at a reversal potential of about -4 millivolts, and then reversed in sign as the inside of the cell was made increasingly more postive. The relation between ACh potential amplitude and membrane potential was nonlinear because of a decrease with depolarization of the peak conductance change produced by the drug.